Ball grid array to prevent shorting between a power supply and ground terminal

ABSTRACT

A semiconductor device manufactured as a ball grid array, chip scale package, or other surface mounting package wherein shorting between a power supply terminal and a ground terminal can be prevented. At least one solder ball functioning as a signal electrode is disposed between a solder ball functioning as a power supply electrode and a solder ball functioning as a ground electrode on the mounting surface of the package.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device, and relatesparticularly to the electrode arrangement of a ball grid array (BGA),chip scale package (CSP), or other multiple pin, surface mountingpackage in which solder balls are used as the external electrodes bywhich connection to an external circuitry is achieved.

2. Description of the Related Art

Manufacturers of memory chips and application-specific IC (ASIC) deviceshave not been able to meet the demand for faster assembly, an increasein the number of pins, and continual reduction in chip size using thequad flat package and other conventional package designs in which pinsare used for the external electrodes. This situation led to thedevelopment of BGA, CSP, and other surface mounting technologies inwhich solder balls are used for external electrodes, thereby alsoachieving thinner, smaller packages with a large number of externalelectrodes. Size is reduced and a large number of external electrodes isachieved in these packages by reducing the pitch between the solderballs functioning as external electrodes to less than 1 mm.

FIG. 7 is a plan view of the mounting surface of a conventionalsemiconductor device as described above. This semiconductor device 100comprises a package 101 with a mounting surface 102 on which are formedsolder balls constituting a plurality of external electrodes. Note that,as shown in FIG. 7, the solder balls formed on the mounting surface 102include a plurality of solder balls 103 a used as a power supplyterminal, a plurality of solder balls 103 b used as a ground terminal,and a plurality of solder balls 103 c, that is, the solder balls otherthan the power supply terminal and ground terminal solder balls, used assignal electrodes.

When the distance between adjacent solder balls is less than 1 mm withthis arrangement, solder shorting and shorting between electrodes causedby fixed or unfixed foreign matter can occur easily during the mountingprocess. Unlike with QFP and other types of pin packages, such shortingcannot be detected by naked eye observations or probing in BGA, CSP, andother types of surface mounting packages. Boundary scanning hastherefore been used as one method of detecting defective connections andelectrode shorting in BGA, CSP, and other types of surface mountingpackages.

Boundary scanning can electrically detect shorts involving signalelectrodes, that is, the external electrodes other than the power supplyand ground electrodes. More specifically, boundary scanning canelectrically detect shorting between signal electrodes, between a signalelectrode and a power supply electrode, and between a signal electrodeand ground electrode. Boundary scanning cannot, however, detect shortingbetween a power supply electrode and ground electrode. This is aparticular problem when, for example, a plurality of solder balls 103 aused as power supply terminals, and a plurality of solder balls 103 bused as ground terminals, are arranged as shown in FIG. 7 with a solderball pitch of 1 mm or less because this arrangement and electrodeproximity can easily result in shorting between a power supply electrodeand ground electrode due to solder debris and other foreign matter.

It should be noted that while its object differs from that of thepresent invention, a semiconductor device disclosed in Japanese PatentLaid-Open Publication No. 6-151688 (1994-151688) teaches the use of alead for external electrodes as a means of preventing transistormisoperation by suppressing the change in power supply potential andground potential as a result of disposing two signal leads between apower supply lead and a ground lead.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to resolve the aboveproblem by providing a semiconductor device formed from a ball gridarray (BGA), chip scale package (CSP), or other surface mounting packagewhereby shorting between a power supply electrode and a ground electrodeis prevented.

A semiconductor device according to the present invention is achieved ina surface mounting package with a plurality of solder balls used asexternal electrodes in an arrangement on the mounting surface such thatpower supply electrodes of different polarity are not adjacent. Thisarrangement makes shorting between a power supply electrode and groundelectrode, which cannot be detected by boundary scanning, more difficultafter mounting to the mounting surface. The boundary scanning detectionrate of shorting between signal electrodes is thereby also greatlyimproved, and the reliability of the mounted semiconductor device canalso be greatly improved.

The pitch between the solder balls of the external electrodes in thesurface mounting package of the present invention is preferably 1 mm orless. Foreign matter such as solder debris inducing shorting betweenexternal electrodes is typically less than 1 mm in size, and even ifshorting between external electrodes results from solder debris or otherforeign matter, shorting occurs between a power supply electrode andsignal electrode or between a ground electrode and signal electrode, anddoes not occur between a power supply electrode and ground electrode.Shorting between these electrodes can therefore be detected by boundaryscanning, and the reliability of semiconductor device mounting cantherefore be greatly improved.

The external electrodes of a semiconductor device according to thepresent invention are further preferably arranged such that at least onesignal electrode that is not a power supply electrode is disposedbetween power supply electrodes of different polarity. Almost allshorting between external electrodes resulting from solder debris orother foreign matter occurs between a power supply electrode and signalelectrode, or between a ground electrode and signal electrode.Considering this, disposing at least one signal electrode that is not apower supply electrode between power supply electrodes of differentpolarity makes shorting between a power supply electrode and a groundelectrode even more difficult. As a result, the reliability ofsemiconductor device mounting can be greatly improved.

Other objects and attainments together with a fuller understanding ofthe invention will become apparent and appreciated by referring to thefollowing description and claims taken in conjunction with theaccompanying drawings, wherein like parts are designated by likereferences.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention willbecome clear from the following description taken in conjunction withthe preferred embodiment thereof and the accompanying drawingsthroughout which like parts are designated by like reference numerals,and in which:

FIG. 1 is a perspective view of a semiconductor device according to apreferred embodiment of the present invention;

FIG. 2 is a side view of the semiconductor device shown in FIG. 1;

FIG. 3 is a side view of a semiconductor device shown in FIG. 1 and FIG.2 when mounted to a mounting substrate;

FIG. 4 is a plan view of the mounting surface of a semiconductor deviceshown in FIG. 1 and FIG. 2;

FIG. 5 is a plan view of an alternative arrangement of the mountingsurface of a semiconductor device shown in FIG. 1 and FIG. 2;

FIG. 6 is a plan view of a further alternative arrangement of themounting surface of a semiconductor device shown in FIG. 1 and FIG. 2;and

FIG. 7 is a plan view of the mounting surface of a semiconductor deviceaccording to a conventional arrangement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiments of the present invention are described belowwith reference to the accompanying figures, wherein FIGS. 1 and 2 areperspective and side views, respectively, of a semiconductor device 1according to the present invention.

As shown in FIGS. 1 to 4, the semiconductor device 1 is a BGA, CSP, orother type of surface mounting package 2 comprising a mounting surface6, as shown in FIG. 4. This mounting surface 6 interfaces with mountingsubstrate 5 in FIG. 3 when the semiconductor device is mounted to amounting substrate. A plurality of solder balls 3 functioning asexternal electrodes of the package 2 are formed on this mounting surface6 at a pitch of 1 mm or less. As a result, a package 2 with a 1.5 cmsquare mounting surface will have more than 150 solder balls 3 formed onthe surface thereof. It should be noted that for simplicity ofillustration a smaller total number of solder balls 3 is shown.

FIG. 3 is a side view of the semiconductor device 1 shown in FIGS. 1 and2 mounted to a mounting substrate 5. A wiring pattern not shown in thefigures is formed on the mounting substrate 5 on the surface thereofinterfacing with the mounting surface 6 of the package 2. The solderballs 3 are thus arranged on the package mounting surface 6 in a patternconforming to the wiring pattern of the mounting substrate 5. Heat isthen applied to thermally fuse and electrically connect the solder balls3 with the corresponding circuit elements of the mounting substrate 5.

FIG. 4 is a plan view of a mounting surface 6 of the semiconductordevice 1. As indicated by the key to FIG. 4, the solder balls 3 formedon the mounting surface 6 of semiconductor device 1 include one or moresolder balls 3 a used as a power supply electrode, one or more solderballs 3 b used as a ground electrode, and one or more solder balls 3 cused as non-power supply and non-ground external signal electrodes.

AS will be known from FIG. 4, the solder balls 3 a to 3 c are arrangedin a specific pattern on mounting surface 6 such that there is at leastone solder ball 3 c used as a signal electrode disposed between anysolder ball 3 a used as a power supply electrode and any solder ball 3 bused as a ground electrode, and no power supply electrode solder ball 3a is thus adjacent to any ground electrode solder ball 3 b.

Solder debris and other foreign matter causing shorting between anyexternal electrodes is generally less than 1 mm in size. In addition,when solder debris or other foreign matter causes a short to an externalelectrode, the short substantially always occurs between a power supplyelectrode and a signal electrode, or between a ground electrode and asignal electrode, and shorts between a power supply electrode and aground electrode occur only with great difficulty. As a result,substantially all shorts involving a power supply electrode can bedetected with boundary scanning.

It should be noted that because the size of solder debris or otherforeign matter causing a short with an external electrode is typically 1mm or less as described above, shorting with a power supply electrodecan be similarly impeded by increasing the distance between the powersupply electrode solder balls 3 a and ground electrode solder balls 3 bwithout disposing a signal electrode solder ball therebetween. Amounting surface 6 exemplary of such alternative configuration is shownin FIG. 5 and FIG. 6.

With the pattern shown in FIG. 5, the signal electrode solder balls 3are arranged such that there is a known gap equal to at least the solderball pitch between any solder balls 3 a and any solder balls 3 b. Thisarrangement similarly reduces the probability of shorting between apower supply electrode and a ground electrode.

With the pattern shown in FIG. 6, the solder ball pitch is increasedonly between the solder balls 3 a and solder balls 3 b. This arrangementalso reduces the probability of shorting between a power supplyelectrode and a ground electrode.

As will be known from the preceding description of a semiconductordevice according to the present invention, at least one solder ball 3 cused as a signal electrode is disposed between any solder ball 3 a usedas a power supply electrode and any solder ball 3 b used as a groundelectrode in the pattern of a plurality of solder balls 3 formed on themounting surface 6 of a semiconductor device 1 according to the presentinvention. As a result, shorting between a power supply electrode and aground electrode after the package 2 is mounted to a mounting substrate5, that is, shorting which cannot be detected by boundary scanning, ismade more difficult, the boundary scanning detection rate of shortsbetween electrodes is greatly improved, and the reliability ofsemiconductor device mounting can be greatly improved.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

Although the present invention has been fully described in connectionwith the preferred embodiment thereof and the accompanying drawings, itis to be noted that various changes and modifications are apparent tothose skilled in the art. Such changes and modifications are to beunderstood as included within the scope of the present invention asdefined by the appended claims unless they depart therefrom.

What is claimed is:
 1. A semiconductor device to be surface-mounted ontoa mounting board, said semiconductor device having a mounting surfacewith a plurality of solder balls arranged at a pitch and isolated fromeach other, said plurality of solder balls including power supply,ground and signal solder balls for connection with power supplyelectrodes, ground electrodes and signal electrodes, respectively, whichare formed on said mounting board in a manner of one to one; each of thepower supply solder balls is surrounded adjacently by a group consistingof the same voltage power supply balls and the signal solder balls andarranged apart from each of the ground solder balls by a distance equalto or larger twice the pitch; and each of the ground solder balls issurrounded adjacently by a group consisting of the ground solder ballsand the signal balls and arranged apart from each of the power supplysolder balls by a distance equal to or larger than twice the pitch. 2.The semiconductor device according to claim 1, wherein the same voltagepower supply balls are concentrically arranged as a power supply solderball cluster in which each of the same voltage power supply balls isadjacent to other same voltage power supply balls.
 3. The semiconductordevice according to claim 1, wherein the ground solder balls areconcentrically arranged as a ground solder ball cluster, in which theground solder balls are adjacent with each other.
 4. The semiconductordevice according to claim 1, wherein the signal solder balls arearranged between two clusters of different voltages.
 5. Thesemiconductor device according to claim 1, wherein any solder balls arenot arranged between two clusters of different voltages.above-identified application.